I installed Mozilla Firefox browser. When ever I use it a white drive looking icon appear on my desktop. I can't "Eject" it without first closing Firefox. As soon as I use Firefox again it appears again.

I believe that you have not completely installed FireFox in the typical way. If I am correct, then this procedure may help you.

Find the FireFox application wherever it is now, and drag and drop it into your Applications folder, or any subfolder under Applications you may choose. This process installs the program. Now you can eject the drive and delete the DMG file that I'm guessing may be on your desktop.

Although I'm a faithful user of FireFox on the PC and under Linux, I've found Safari to be a very pleasant browser and I have not installed FireFox on my mini, yet.